In most current color picture tube types, a peripheral frame supporting a shadow mask is suspended in a faceplate panel by means of springs that are welded either directly to the frame or to plates which in turn are welded to the frame. In the directly welded version, the springs are made of bimetallic materials; and in the plate version, the plates are bimetallic. As the springs or plates become heated by transfer of heat from the mask through the frame, the bimetallic materials expand differently, thereby bending the springs or plates to cause movement of the mask-frame assembly toward a screen disposed on the panel.
It is common to use either three or four springs to support a mask-frame assembly within a rectangular faceplate panel of a tube. In a three-spring support system, one spring is usually located at the upper center of the mask, and the other two springs are located along the sides of the tube between the centers of the sides of the mask and the lower two corners of the mask. In a four-spring support system, springs are usually located at the top and bottom centers of the mask and at the left and right centers of the mask. In both the three- and four-spring support systems, as described above, it is possible for the mask-frame assembly to twist slightly and shift relative to the faceplate, during manufacturing and tube operation.
A known means for minimizing twisting and shifting of a mask-frame assembly uses spring supports at the four corners of the frame. Embodiments for achieving such corner support are shown in U.S. Pat. No. 4,723,088, issued to Sone et al. on Feb. 2, 1988, and in U.S. Pat. No. 4,728,853, issued to Sone et al. on Mar. 1, 1988.
U.S. Pat. No. 4,723,088 shows a mask frame having truncated corners with supports at each corner. The supports are bent plates including three sections A first section is welded to the frame. A second section extends at an angle from the first section toward a skirt of a faceplate panel. A third section extends from the second section. The third section includes an aperture that engages a metal stud that is embedded in the panel sidewall.
U.S. Pat. No. 4,728,853 discloses a support which includes two members welded together. One member, having a flat plate shape, is welded at several separated points to a mask frame. The second member includes three sections. A first section is welded to the first member. A second section angles from the first section, and an apertured third section engages a support stud in the panel sidewall.